Cross rams in a blowout preventer, that is, rams which have at least two opposed pairs, are disclosed in U.S. Pat. No. 3,554,480 to Rowe as inventor and assigned to Cameron Iron Works, Inc. As discussed in that patent, an advantage of a cross ram is the flexibility in, for example, providing pipe-type rams which close around an oil-well drilling pipe or blind rams which block the well completely. Other major advantages of a cross-type ram is the reduction in the so-called blowout preventer stack height and weight.
More specifically, as is well-known in the oil-well drilling art, for safety purposes many different ram functions are desired when drilling a well. To accomplish these many functions, both cross rams and for that matter the more typical single ram pair are stacked one on top of the other sometimes requiring stacks of six dual rams. Because of the high pressures involved, the bodies of the preventers are relatively thick and thus the distance from the wellhead to the drilling deck is very large. A typical distance might be more than 45 feet. In addition, a large stack of blowout preventers has a very heavy weight and may tend to stress the wellhead. A two-unit stack of dual-type blowout preventers is shown in Allen U.S. Pat. No. 2,912,214. The bulk of the body and its height is quite apparent.
Thus, the cross ram discussed above is a partial answer to the problems of flexibility and both blowout stack height and weight. But there are remaining problems of flexibility, pressure resistance which is very great in oil-well environments and ultimate stack heights.
Thus, it is an object of the present invention to provide an improved blowout preventer.
It is a more specfic object to provide a blowout preventer which is more flexible and has more functions on one level.
It is another object of the invention to provide a blowout preventer which has a great number of functions but yet a relatively lower stack height.
It is another object of the invention to provide increased pressure capabilities without increasing the overall size and weight of a preventer component.
In accordance with the above objects, there is provided a blowout preventer comprising a substantially spherical body having a vertical bore for accommodating a drill string of an oil or gas well and first and second pairs of opposed bores radiating laterally in a common plane from the vertical bore. First and second pairs of replaceable sleeve-like ram guideways are inserted respectively into the first and second pairs of opposed bores. A pair of rams are reciprocable in each pair of the guideways for selectively sealing the vertical bore.
From a method standpoint, apparatus is provided as above and the first and second pairs of ram guideways are selected from a plurality of guideways each having different interior configurations. The selected guideways accommodate different types of rams. These guideways are then inserted into the first and second pairs of opposed bores of the blowout preventer and compatible-types of rams are then placed therein.